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Microcontroller based Fan speed controller by measuring Temperature

1. Introduction

Measuring the impact of environmental constraints is analysis and control.

Different types of data loggers and data acquisition system are available in the

market to perform this task well.

Temperature measurement is today more common. The ambient

temperature keeps varying during different times of the day and night at

different places. Temperature measurement can be done for weather forecast

or for automation in electronics devices and industries.

Here we describe a temperature measurement device which controls the

speed of the FAN using microcontroller AT89S52, temperature sensor and other

components. The temperature is measured at a user defined interval. Each time

the current temperature goes above ie increase or decrease corespondigly the

FAN speed will vary .

1Government Polytechnic Tumkur


2. Block Diagram

The above Block diagram consist of the following Functional Blocks

1. Temperature sensor

2. Analogue to digital converter ADC

3. Micro controller

4. Power supply

5. Lcd module

6. Motor Driver & DC motor FAN

1.Temperature sensor:-

This section has a temperature sensor which measures the temp and

gives particular analog output. And gives output to the ADC.



2. Analogue to digital converter adc

Analog to digital converter which takes input from the temperature

sensor and Converts it into digital signals, these signals are send to the

processor.

3.Microcontroller:-

Microcontroller is the heart of the circuit which receives the digital signals

from the ADC and converts it into the ASCII code and gives the measured

temperature on the Display.

4. Power supply:-

The most of the Digital IC’s Microcontrollers, diplay’s, etc are work only in

+5V so power supply circuit it must needed with some typical components. The

relay requires unregulated DC supply so the power supply for the relay section

is unregulated 12 V.

5. LCD module:-

The LCD is used for display the temperature measured. And it also

displays the fan speed mposition .

6. Motor Driver:

This driver circuit uses L293D IC for controlling speed of the DC motor

FAN and the speed of the DC motor can be controlled by inputting the PWM

signals from the micro controller. And the direction of the motor is also can

be controlled by alternating the inputs to the IC.



3. Parts List

IC1 AT 89S52 microcontroller

IC2 ADC 0804 analogue-to digital converter

IC3 LM35 temperature sensor

IC4 7805 5v regulator

IC5 L293D motor driver

BR1 Bridge rectifier 1A

Resistors (all of ¼ watt, +/- 5 % carbon)

R1,R4 330-ohm

R2,R3,R5-R8 10 kilo-ohm

RNW1 10kilo-ohm resistor network

VR1 10 kilo-ohm variable

VR2 1 kilo-ohm variable

Capacitors

C1 1000uF,25v electrolytic

C2 0.1 uF ceramic disk

C3 10uF,16V electrolytic

C4,C5 33 pF, ceramic disk

C6 150pF, ceramic disk

Miscellaneous

X1 230V AC Primary to 12V, 500mA secondary transformer

Xtal X1 12Mhz

S1-S4 Push-to-on switch

PZ1 Piezo Buzzer

LCD module 16 character x 2 line LCD module

FAN 12 V DC motor



4. Circuit diagram

5. Hard ware Description



Micro-controller at89s52

Features

• compatible with mcs®-51 products

• 8k bytes of in-system programmable (isp) – endurance: 10,000 write/erase

cycles

• 4.0v to 5.5v operating range

• fully static operation: 0 hz to 33 mhz

• three-level program memory lock

• 256 x 8-bit internal ram

• 32 programmable i/o lines

• three 16-bit timer/counters

• eight interrupt sources

• full duplex uart serial channel

• low-power idle and power-down modes

• interrupt recovery from power-down mode

• watchdog timer

• dual data pointer

• power-off flag

• fast programming time

• flexibleisp programming (byte and page mode)

• green (pb/halide-free) packaging option

description

The at89s52 is a low-power, high-performance cmos 8-bit microcontroller

with 8k bytes of in-system programmable flash memory. The device is

manufactured using atmel’s high-density nonvolatile memory technology and is

compatible with the indus-try-standard 80c51 instruction set and pinout. The

on-chip flash allows the program memory to be reprogrammed in-system or by

a conventional nonvolatile memory pro-grammer. By combining a versatile 8-bit



cpu with in-system programmable flash on a monolithic chip, the atmel at89s52

is a powerful microcontroller which provides a highly-flexible and cost-effective

solution to many embedded control applications. The at89s52 provides the

following standard features: 8k bytes of flash, 256 bytes of ram, 32 i/o lines,

watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector

two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and

clock circuitry. In addition, the at89s52 is designed with static logic for

operation down to zero frequency and supports two software selectable power

saving modes. The idle mode stops the cpu while allowing the ram,

timer/counters, serial port, and interrupt system to continue functioning. The

power-down mode saves the ram con-tents but freezes the oscillator, disabling

all other chip functions until the next interrupt or hardware reset.

Oscillator

Xlt1 and xlt2 are the input and output of an inverting amplifier, which is

used as a crystal oscillator, in the pierce configuration by connecting an

external crystal. A 11.0592mhz crystal is selected which provides a internal

cycle timing of 1μsec (1mhz) which is 1/12 of the oscillator frequency.

The clock generator divides the oscillator frequency by 2, and provides a

two-phase clock signal to the chip. The phase1 signal is active during the first

half of each clock period, and phase2 signal is active during the second half of

each clock period.

Reset circuit

Reset of the micro-controller chip is accomplished by holding the reset pin

high for at least two machine cycles (24 oscillator periods) while oscillator is

running. The cpu responds by executing an internal reset. The internal reset is

executed during the second cycle in which reset is high and is repeated every

cycle until reset goes low.



An automated reset can be obtained when vcc is turned on by connecting

the reset pin to a 10k resistor and 1μf capacitor

When power comes on, the current through the resistor commences to

charge the capacitor. The voltage at reset is the difference between vcc and the

capacitor voltage, and decreases from vcc as the capacitor charges. The larger

the capacitor is, the more slowly the voltage at the reset pin falls. The time

required is the oscillator start up time plus 2 machine cycles. If the vcc rise-time

is less than 1msec and the oscillator startup time does not exceed 10msec, a

1μf capacitor will provide a reliable power on reset.

IC LM35 (IC3) is a three-terminal precision temperature sensor whose

output voltage is linearly proportional to the Celsius temperature with +/- 10.0

mV/ C scale factor. It thus has an advantage over linear temperature sensors

calibrated in degree Kelvin, and the user is not required to subtract large

constant voltage from its output to obtain convenient Centigrade scaling.

The LM35 does not require any external calibration or trimming to

provide typical accuracies. It is rated for full -55 C to 150 C ranges and

operates off 4V-30V input. It gives 0V output for 0oC temperature .The analog

output (Vout) at pin 2 of LM35 is fed to Vin (+) pin 6 of analog-to-digital

converter ADC0804,whose Vin (-) pin is connected to ground .Pin 1 of LM35 is

connected to 5V supply and pin 3 is grounded.

ADC0804 (IC2) is a CMOS, 8-bit single channel analog-to-digital

converter .It features conversion time of less than 100ms , differential analog

input voltage, TTL-compatible inputs and outputs, on-chip clock generator ,

analog voltage input range from 0V to 5V , and no zero adjustment . The

conversion time depends on resister R3 and capacitor C6. The conversion rate

in free running mode is 640 kHz. Digital and analog ground should be separated

in ADC0804 to avoid any interference in the circuit.



The resolution of 8-bit ADC0804 is 19.53 mV, which doesn’t match with

the scale factor cf LM35 and therefore can cause error. To avoid this error, the

full-scale range of ADC0804 is made 0-2.56V by adjusting the voltage at pin 9

(Vref/2) to 1.28V through 1-kilo-ohm preset VR2. In ADC0804, the input analog

voltage is divided by its step size to give digital output. For each 10 mV rise and

fall of the analog input at Vin (+), digital outputs at DB0 through DB7 increase

and decrease, respectively. The maximum input voltage that can be converted

by the ADC is 2.55v (10mV * 255), giving full-scale output of FF hex value in this

system.

The 8-bit digital output of ADC0804 (DB0 through DB7) is connected to 8-

bit port P0 of the microcontroller. Signals , and of the ADC are connected

to P2.7, P2.6 and P2.5 of the microcontroller. These signals of the ADC act as

handshaking signals with microcontroller IC1. and are the input pins of

the ADC, while is the output pin. Through signal, the

microcontroller gets to know when the conversion from analog into digital is

completed by the ADC.

The microcontroller makes WR pin ‘low’ RD and pin ‘high’ to start the

conversion. Pin INTR goes high for the end oh conversion. A transition from high

to low on INTR indicates end of conversion. Then the microcontroller makes RD

‘low’ and WR ‘high’ to read the 8-bit data at DB0 through DB7 through

microcontroller port P0. Through its firmware, the microcontroller multiplies the

digital input at port 0 with the steps size value of ADC0804 and then divides

with the temperature / volt scale factor of LM35 to give the measured and

calibrated oC temperature.

The measured temperature is instantaneously displayed on the LCD. Port

P1 of the microcontroller is connected to data port as well as The handshake

signals of the LCD (RS, R/W and Enable) , respectively. All the data is sent to the

LCD in ASCII form to display. Only the commands are sent in hex form to the



LCD. RS signal is used to distinguish between data (RS=1) and command

(RS=0). Use Present VR1 to control the contrast of the LCD.

The motor driver circuit is connected to Port 3 which needs 3 pins i.e

enable, Input 1 & input 2 of L293D IC5. By enabeling pin we can run the FAN.

Rotating the FAN by giving input 1 is high & input 2 is low & by giving pulse or

PWM (pulse width modulation) signals the enable pin we can control the speed

of the FAN. The speed is depends up on the on period of the enable signal.

For proper measurement, adjust preset VR2 to give 1.28V at pin 9 of the

ADC. Initially, using preset VR1set the contrast level for display on LCD.

Power supply: -

The 230V, 50Hz AC mains power supply is stepped down by transformer

X1 to deliver a secondary output of 12V at 500mA. The transformer output is

rectified by a full-wave bridge rectifier BR1, filtered by Capacitor C1, and

regulated by IC 7805. The output of IC 7805 which is 5V used for operation of

the circuit. The ripple in the regulator output is filtered by capacitor C2. For the

DC motor the supply is taken before the regulator.



6.Software section

Software operation flow chart

YES NO

YES


INITIALISE SP AND LCD

DISPLAY WELCOME MESSAGE

Start the temerature measuring

INITIALISE NUMBER OF

SAMPLES TO ZERO

START ADC WR=0>1 INTR=1

INTR=1

?

READ ADC RD=0

CONVERT ADC OUT TO TEMPERATURE ASCII VALUE

INCREASE NUMBER OF SAMPLES BY ONE

DISPLAY TEMPERATURE AND NUMBER OF SAMPLES

DELAY ACCORDING TO MEASURING INTERVAL

TEMP>

increase speed Decrease speed


NO

Source code:

The software is well commented and easy to understand. Written in C-

language and assembled using Keil uvision -3, it works as per the flowchart

shown in Fig. The hex code generated by the keil is burnt into the

microcontroller using a suitable programmer.

The value of the measured temperature and the number of samples taken

until power-‘on’ are displayed on the LCD screen. The number of samples is

updated according to the measuring interval.

Each port of the microcontroller is made input through software by

putting high on the respective pin or port. By default, all the ports act as output.

Instead of using timer, nested loops are used to provide delay at various

locations of the software. The values for the loop are calculated according to

the crystal frequency and the machine cycles taken by the used instructions.

Program:

#include "lcd.h"

#define adc_input P1

#define sec 100

sbit wr= P3^1;

sbit rd= P3^0;

sbit intr= P3^2;

sbit m1= P3^3;



sbit m2= P3^4;

sbit en1=P3^5;

int s,temp_new;

unsigned char i,j;

int test_intermediate3=0,

test_final=0,test_intermediate1[10],test_intermediate2[3]={0,0,0};

void delay(unsigned int msec )

{

int i ,j ;

for(i=0;i<msec;i++)

for(j=0; j<1275; j++);

}

void shape() // Function to make the shape of degree symbol

{

lcd_cmd(64);

lcd_data(2);

lcd_data(5);

lcd_data(2);



lcd_data(0);

lcd_data(0);

lcd_data(0);

lcd_data(0);

lcd_data(0);

}

void convert() // Function to convert the values of ADC into numeric value to

be sent to LCD

{

lcd_cmd(0x80);

lcd_str("Temp Base FAN SC");

delay(2);

test_final=(((9*test_intermediate3)/5)+32);

s=test_final/100;

test_final=test_final%100;

lcd_cmd(0x88);

test_final=test_intermediate3;

lcd_cmd(0xc1); //Setting cursor to first position of first line

delay(2);



lcd_str("TEMP:");

s=test_final/100;


lcd_cmd(0xc8);

if(s!=0)

lcd_data(s+48);

else

lcd_cmd(0x06);

s=test_final/10;


lcd_data(s+48);

lcd_data(test_final+48);

lcd_data(0);

lcd_data('c');

lcd_data(' ');

delay(2);

}

void delaym(unsigned int value)

{

unsigned char y;



for (y=0; y<value; y++) ;

}

void main1()

{

adc_input=0xff;

delay(2);

lcd_init();

delay(2);

m1=1;

m2=0;

en1=0;

for(j=0;j<3;j++)

{

for(i=0;i<10;i++)

{

delay(2);

delay(1);

rd=1;



wr=0;

delay(1);

wr=1;

while(intr==1);

rd=0;

lcd_cmd(0x88);

test_intermediate1[i]=adc_input/10;

delay(1);

intr=1;

}

for(i=0;i<10;i++)

test_intermediate2[j]=test_intermediate1[i]+test_intermediate2[j];

}

test_intermediate2[0]=test_intermediate2[0]/3;



test_intermediate3=test_intermediate2[0]+test_intermediate2[1]+test_int

ermediate2[2];

shape();



convert();

temp_new=s*10+test_final;

}

void delayms2(int usec)

{

for (i=0;i<usec;i++);

}

void delayms1(int msec)

{

for (i=0;i<msec;i++)

for (j=0;j<1275;j++);

}

void main()

{

m1=1;

m2=0;

while(1)



{

main1();

while(j<20000)

{

en1=1;

delayms2(150-temp_new);

en1=0;

delayms2(150-temp_new);

}

}

}



7.PCB layouts

7.1 Bottom Side of PCB

7.1 Top Layer of PCB



7.2 3D view of PCB layout



8.Conclusion

This project is an effort to demonstrate the worthiness of Atmel 89S52 IC

for the operation of measuring temperature. It has own limitations which are

very common in any of the project works from junior level technicians. The

maximum temperature can measured by this project is 1500c and minimum is -

550c only. With these draw backs this project is only used for areas such as

1. Measuring temperature in home or room.

2. Whre the power consumption is the main issur there by using our

project the power can be saved like places Mobile towers.

Although this project is just a simple of the capabilities of At 89S52 from Atmel

corporation. With the forthcoming series of Atmel IC’s from the company one

can expect larger storing of system software and high operating speeds.



9. Bibliography

1. Electronics For You of month September 2008

2.www.rickyworld’s.info

3.www.8051projects.info

4. www.scienceprog.in

5. www.circuittoday.com

6. The 8051 microcontroller and embedded systems

Mazdi & Mazdi

5. www.alldatasheet.com

6. www.8051projects.net

7. www.microcontrollerprojects.com

8. From the book “hobby circuit”.

Please add datasheets how much you want

After read this, delete these two lines.


http://www.rickyworld's.info

http://www.microcontrollerprojects.com/

http://www.8051projects.net/

http://www.alldatasheet.com/

http://www.circuittoday.com/

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